Endocrine 5

Question 1

What are the functions of calcium within the body?

Answer 1

1. Maintain structural integrity of bones + teeth 2. Intracellular messenger or regulatory ion

Question 2

Describe the two mechanisms by which intestinal absorption of calcium occurs:

Answer 2

Intracellular: - ATPase pump @ basal membrane - Non saturable transport - Depends on dietary calcium level Affected by complexation of excess Ca with anions Transcellular: - Vit D dependant - Saturable transport - Calcium channel at luminal membrane (unregulated by Vit D)

Question 3

Briefly describe the two ways that calcium is re-absorbed via the kidney:

Answer 3

Ca2+ passes freely through glomerular filtration barrier - about 70% of Ca2+ is re-absorbed via Na+-Ca2+ co-transport system About 20% filtered calcium is reabsorbed in ascending limb of loop of Henle + remaining 10% in distal tubule - done by PTH

Question 4

Describe the components of serum total calcium:

Answer 4

Free calcium (50%) Complexed calcium (5%) Protein-bound calcium (45%)

Question 5

What blood anticoagulants bind to Ca2+ should be avoided?

Answer 5

EDTA Citrate Oxalate

Question 6

Name a condition where this would be seen:

Answer 6

Hyperphosphataemia (or oxalate)

Question 7

Name a condition where the following presentation would be seen:

Answer 7

Acidosis - normal total Ca with increased Ca++ and decreased albumin bound

Question 8

What two neoplasms cause pseudo-hyperthyroidism in dogs?

Answer 8

1. Lymphoma (usually T-cell)
2. Apocrine gland of the anal sac carcinoma

Question 9

What are the two main ways that hypercalcaemia arises?

Answer 9

1. Increased Ca2+ mobilisation from bone/absorption from intestine - pseudo-hyperparathyrodism
2. Decreased urinary excretion of Ca2+ - renal failure (rare in dogs and cats), thiazide diuretics, hypoadrenocorticism - about 30% of dogs with hypoadrenocorticism are hypercalcemic

Question 10

What could cause primary hypoparathyrodism?

Question 11

What are the three main ways that hyperphosphatemia can arise?

Answer 11

1. Decreased urinary PO4 excretion - decreased GFR, urinary bladder rupture, hypothyroidism
2. Increased PO4 aborption from intestine - excessive Vitamin D (endogenous or exogenous), excessive dietary P (all meat diet)
3. Shift of PO4 from ICF to ECF - myopathies, tumour lysis syndrome

Question 12

What are the main causes of hypophatemia?

Answer 12

1. Increased urinary PO4 Excretion - prolonged diuresis, PTH or PTHrp
2. Decreased PO4 absorption from intestine - hypovitaminosis D or anorexia/mal